Power system disturbances, such as line tripping and drop of generation, cause local and inter-area power system oscillations. Usually, local oscillation modes range in frequency from 0.7 to 2.0 Hz. Inter-area oscillation, which refers generally to a group of generators in one area that swing against a group of generators in another area, normally ranges in frequency from 0.1 to 0.8 Hz. The local oscillation involves a few generators within a small portion of a power system and has little impact on an overall power system. Inter-area oscillations constrain the amount of power that can be transferred through some parts of interconnected power grids. Without proper remedial actions, inter-area oscillation can result in power system separations or major blackouts.
Wide-Area Measurement Systems (WAMSs) are used to monitor power system disturbances. WAMSs generally include among other things phasor measurement units (PMUs), phasor data concentrators (PDCs), visualization software and data archiver software. PMUs, or relays with phasor measurement capabilities, are placed at various locations of the power system to acquire voltage and current phasor measurements therefrom. These PMUs may be adapted to time-stamp such data. PDCs may be adapted to collect the phasor measurements from the PMUs and time-align such data. Using visualization and data archiver software, the power system may be monitored using phasor measurements acquired by the PMUs. In this way, WAMSs generally provide real-time information relating to transmission line power flows, bus voltage magnitude and angle, and frequency measurements across the transmission network. WAMSs also provide information for post-mortem analysis (e.g., power system modal analysis for determining inter-area oscillation).
With similar system architecture, Wide-Area Control Systems (WACS) and Wide-Area Protection Systems (WAPS) have also been used to control devices within the power system. For example, FIG. 1 illustrates a prior art system which uses time-correlated data to monitor and control power systems. The system of FIG. 1 generally comprises a plurality of PMUs 100a, 100b, 100c; a PDC 102; a control unit 104 and a command unit 106. The PMUs 100a, 100b, 100c are placed at various locations of the power system to acquire voltage and current phasor measurements therefrom. These PMUs may be adapted to time-stamp such data. The PDC 102 is adapted to collect the phasor measurements from the PMUs and time-align such data. A control unit 104 is provided to generally process the time-aligned data and determine whether the command unit 106 should send a subsequent command to appropriate power system devices or power system elements for protection and/or control functionality (e.g., shed generation, insert a system braking resistor or control a Static VAR Compensator). Nevertheless, the complex system illustrated in FIG. 1 consists of a disjointed and fragmented collection of devices that make the system unreliable and difficult to implement.
Several desired benefits of the preferred embodiments, including combinations of features thereof, of the invention will become apparent from the following description. It will be understood, however, that an arrangement could still appropriate the claimed invention without accomplishing each and every one of these desired benefits, including those gleaned from the following description. The appended claims, not these desired benefits, define the subject matter of the invention. Any and all benefits are derived from the multiple embodiments of the invention, not necessarily the invention in general.